Effects Of Simulated Deposition Of Nitrogen And Phosphorus And Litter Treatments On Soil Organic Carbon In Pinus Koraiensis Forest

Nitrogen and phosphorus are nutrients for plant growth in forests.Litter can provide nutrients that plants need for growth and development.As an important forest resource,Pinus koraiensis forest maintains and regulates the material cycle and energy flow of the ecosystem.However,the rapid increase of nitrogen and phosphorus in the atmosphere caused by human activities has affected the amount of plant litter and soil organic carbon,thus disrupting the balance of the carbon cycle.In addition,litter can affect soil fertility,plant growth and development,and ecosystem productivity by affecting soil organic carbon.Therefore,this study took Pinus koraiensis plantation and broadleaved Pinus koraiensis forest as the objects,and set 3 plots for each forest type,with 12 plots in each plot.Each quadrat performs two treatments.（1）Litter treatment:removal（R）,addition（A）and control（CK2）levels;（2）Simulated nitrogen and phosphorus deposition treatment（hereinafter referred to as nitrogen and phosphorus treatment）:From May to September in 2018（the first year of the experiment）and 2019（the second year of the experiment）,（NH₄）₂SO₄ and（NH₄）₂HPO₄ were used as nitrogen source and phosphorus source respectively.Low concentration（L）,medium concentration（M）,high concentration（H）and control（CK1）levels were set.In May,August and October of 2018 and 2019,3 sampling sites of 30 cm×30 cm were randomly selected in each plot.Soil samples of 0～20 cm were collected from each plot to measure the content of soil organic carbon components and explore the differences of nitrogen and phosphorus and litter treatment in different Pinus koraiensis forests.The aim of this study was to elucidate the effects of nitrogen and phosphorus and litter treatments on soil organic carbon in two Pinus koraiensis forests.The main results are as follows:（1）The contents of soil total organic carbon,inert organic carbon,particulate organic carbon,easily oxidized organic carbon and the ratio of humic acid to fulvic acid were the highest under medium concentration of nitrogen and phosphorus treatment.The contents of light fraction organic carbon,humin organic carbon and the ratio of humic acid to humus extract were the highest under high nitrogen and phosphorus treatment.The contents of soil humus extract organic carbon and humic acid organic carbon were the highest under nitrogen and phosphorus free treatment.The content of fulvic acid organic carbon in soil was the highest under low concentration of nitrogen and phosphorus.（2）Under litter removal,soil total organic carbon,inert organic carbon,fulvic acid organic carbon,humin organic carbon and light fraction organic carbon content were the highest;Litter addition treatment can increase soil particulate organic carbon and easily oxidized organic carbon content.Litter treatment could promote the release of humus extract organic carbon and humic acid organic carbon,and decrease humic acid to fulvic acid and soil humic acid to humus extract.（3）In two Pinus koraiensis forests,the contents of soil total organic carbon,particulate organic carbon,inert organic carbon,easily oxidized organic carbon,fulvic acid organic carbon and humin organic carbon decreased by 11%,12%,11%,12%,35%,25%and 24%in the second year compared with the first year,respectively.The contents of light fraction organic carbon,humus extract organic carbon and humic acid organic carbon increased by 59%,29%and 60%,respectively.In conclusion,nitrogen and phosphorus treatments and litter treatments can promote the accumulation and release of soil organic carbon and humus,and change the degree of humification of soil organic matter and the quality of soil humus.The experimental years had significant effects on soil organic carbon and humus organic carbon in Pinus koraiensis forest.